1. Field of the Invention
This invention relates to recording apparatus such as copying apparatus and facsimiles, and more particularly to an inexpensive and simple recording and apparatus capabale of recording an image on a sheet of plain paper without using a special recording sheet such as, for example, a copying sheet treated with a photoconductive material such as zinc oxide.
2. Description of the Prior Art
Prior art recording apparatus of this kind employed a wide variety of methods which had their respective merits and demerits.
In one type of such facsimile apparatus, a recording method of this kind utilizing the breakdown due to an electric discharge has been in use for quite a long time, which method includes providing a white surface coating on a carbon black layer and electrically destroying the white surface layer to obtain a record. This electric discharge recording method has been defective in that it requires a special recording sheet which is quite expensive, gives off fumes that are accompanied by bad odors which are produced from the recording sheet during recording and products of the breakdown due to the discharge tend to become attached to the recording stylus.
Another type of facsimile apparatus employs a method of the kind in which a color is produced by electrolysis. According to this electrolytic recording method, a material which develops a color when subjected to electrolysis is coated on a recording sheet and a signal voltage is applied to the recording sheet through a recording stylus so that a colored record can be obtained by the electrolytic reaction which takes place at the portions applied with the voltage. The electrolytic recording method has been defective in that a special expensive material must be coated on a recording sheet and, since it includes a wet process, a record of high density and resolution cannot be obtained owing to the blurring of the recorded image. The electrolytic recording method has further been defective in that a special expensive material must be coated on a recording sheet and, since it includes a wet process, a record of high density and resolution cannot be obtained owing to the blurring of the recorded image. The electrolytic recording method has further been defective in that the record obtained tends to undergo a change due to aging since the color is produced by a chemical change, and the recording sheet tends to be chemically affected by other sheets during the storage thereof with the result that the recorded image is also subject to a change.
An electrostatic recording method has been advantageous over these methods in that a record can be reproduced on a recording sheet by relatively simple means and an improvement in the picture quality can be expected. However, the electrostatic recording method has been disadvantageous in that not only a special expensive recording sheet called an electrostatic recording sheet is required, but also an extra process of developing and fixing after making the recording is required compared with the above-mentioned recording method which utilizes the breakdown of an electric discharge, or color production by electrolysis, and the requirement for these extra process leads to complex apparatuses.
Other methods employed heretofore include converting a signal into mechanical vibrations and striking a recording sheet through carbon paper by means actuated by mechanical vibrations thereby to obtain a record, or using a special recording sheet (a pressure-sensitive sheet) which produces a color in response to pressure. These methods have however been defective in their poor frequency response and in the trouble of requiring such a special sheet.
Silver salt photography is another recording method employed heretofore in the art. This method has however been unfit for practical use except for applications to very special purposes where a high recording performance is required, because the recording material itself is very expensive. Materials employed in copying apparatus and the like will now be discussed. Electrofax is an optical recording method which employs a recording sheet prepared by coating a mixture of a photoconductor such as zinc oxide and a special resin binder on a sheet of paper. Thus, this method also requires a specially processed recording sheet. Further, there is a recording method employing a heat-sensitive recording sheet which is expensive and specially processed. Thus, the problem of expensiveness of the recording sheet is still left unsolved in these methods.
Diazo-type copying apparatus is one typical example of copying apparatus of simple construction using a relatively inexpensive recording sheet. In spite of the fact that this apparatus is very favorable for the reproduction of an original in sheet form by exposure to transmitted light, it has been defective in that its application is limited due to the inability to carry out the reflection copying of articles, such as books and the reproduced record cannot be preserved for an extended period of time due to discoloration or disappearance of the image since a chemical material is used.
Xerography is an inexpensive and favored method in the point that a highly accurately reproduced record can be obtained in spite of the use of a sheet of plain paper. However, this method has had the disadvantge that the plate or drum of photoconductive selenium used therein is quite costly and mechanically brittle and therefore extreme care must be taken in the handling thereof. Further, for the successful electrostatic transfer printing of a toner image onto a sheet of plain paper, very complex handling and expensive means have been required since the remaining toner image must be swept off by means such as a soft brush or a vacuum sweeper to prepare for the next copying cycle.